In recent years, the techniques for obtaining still images from moving images at any given point in time when the moving images captured by video cameras are being reproduced to reproduce the still images have been developing. For example, there are cases where still images at a predetermined point in time are reproduced according to an instruction by the user and others, during the time when moving images of golf swing, etc. are being reproduced.
Normally, moving images are captured at a slow shutter speed by lengthening exposure time for imaging elements, so that the successive images have motion blur. The motion blur obtained by lengthening the exposure time enables capturing of smooth video as moving images. Although moving images with smooth motion can be captured at a slow shutter speed, sharp still images with less motion blur cannot be obtained when the still images are extracted from the moving images.
Conversely, still photo images are captured at a shutter speed faster than that when moving images are captured by video cameras. Thus, motion blur, such as subject blur and hand shake blur, can be suppressed by releasing the shutter at a fast speed and shortening the exposure time. Although sharp still images with less motion blur can be obtained at a fast shutter speed, unnatural moving images as if reproduced on a frame by frame basis are obtained when sill images are successively reproduced as moving images.
Accordingly, when moving images and still images are simultaneously captured, only still images with motion blur can be obtained by prioritizing smoothness in the moving images, and the smoothness in the moving images will be lost by prioritizing the image quality of the still images.
Furthermore, still images captured at a fast shutter speed, that is, images captured for shorter exposure times result in dark images with narrower dynamic ranges as a whole. Here, when gain is increased to make brighter the images captured for shorter exposure times, the images will have a smaller S/N ratio and visible noise.
The conventional capturing/recording apparatus that simultaneously captures moving images and still images captures successive images with less motion blur at a faster shutter speed. Here, the apparatus calculates a motion vector based on the relationship between previous and subsequent frames, and records the calculated motion vector together with the images. As such, the technique has been disclosed which reproduces moving images by adding motion blur to the images based on the motion vector, so that smoothness is added to the moving images, and which reproduces still images with less motion blur without performing any processing on the still images (for example, see PTL 1). FIG. 1 is a block diagram illustrating a configuration of a conventional image-capturing/recording apparatus 10 described in PTL 1.
In FIG. 1, a high speed camera 11 is a camera that captures an image at a shutter speed faster than normal cameras. The “high speed” herein is a shutter speed at which sharp still images with less subject blur can be obtained, and a shutter speed at which moving images successively reproduced result in displaying of intermittent unnatural motion.
A memory 12 stores the images captured by the high speed camera 11. The images stored in the memory 12 are transferred to an MV calculating unit 13 and a motion blur adding unit 14. The MV calculating unit 13 calculates a motion vector between the images read from the memory 12. The calculated motion vector is in transmitted to an MV coder 16.
The motion blur adding unit 14 reads video stored in the memory 12, calculates motion blur using the motion vector calculated by the MV calculating unit 13, and adds the calculated motion blur to the read video. The video to which the motion blur has been added is output to a video coding unit 15.
The video coding unit 15 codes image information to which the motion blur adding unit 14 has added the motion blur, as video information. The coded video information is output to a multiplexing unit 17. The MV coder 16 codes the motion vector calculated by the MV calculating unit 13.
The multiplexing unit 17 multiplexes the coded information. The multiplexed information is recorded by a recording unit 18.
With the configuration, the image-capturing/recording apparatus 10 captures images using a high-speed shutter, estimates a motion vector (MV), and codes and records each frame image and the motion vector. Then, the image-capturing/recording apparatus 10 obtains sharp still images with less motion blur by capturing the images using the high-speed shutter, and estimates the motion vector with high precision. The image-capturing/recording apparatus 10 records the video to which the motion blur has been added using the motion vector, together with the motion vector that has been used to add the motion blur.
Furthermore, there exists (i) a unit for obtaining a wide dynamic range image by synthesizing images captured for different exposure times with respect to an image with a small exposure amount, as images captured using the high-speed shutter, and (ii) a technique for correcting the dynamic range image according to the motion of a subject when the images are synthesized (for example, see PTL 2). FIG. 2 is a block diagram illustrating a configuration of a conventional image capturing apparatus 20 described in PTL 2.
In FIG. 2, an A/D converter 21 amplifies an analog output of imaging elements and converts it into digital data. Here, a short-time exposure image data item and a long-time exposure image data item of the same subject are captured by CCD imaging elements, and are temporarily stored in an SE memory 22 and an LE memory 23, respectively.
Next, the SE memory 22 and the LE memory 23 transmit the image data items to a CPU 29. Then, a motion estimation unit 30 estimates motion of the subject based on two image data items with different exposure amounts.
When the motion estimation unit 30 does not estimate the motion, a multiplier 24 multiplies an exposure amount ratio between a short-time exposure image and a long-time exposure image by the short-time exposure image data item read from the SE memory 22. A synthesizing circuit 25 forms a wide-dynamic-range synthesized image using the multiplied short-time exposure image data item and the long-time exposure image data item read from the LE memory 23. A compression circuit 26 synthesizes and compresses the wide-dynamic-range synthesized image, and outputs, the resulting image through a selector 28 controlled by the CPU 29.
When the motion is estimated, the long-time exposure image data item which is read from the LE memory 23 and in which signal processing, such as γ correction and edge enhancement, is performed by a signal processing circuit 27 is output through the selector 28.
Thereby, the wide dynamic range synthesized image is obtained when two images are captured with different exposure amounts, and the motion of the subject is corrected when the subject moves.